The Structure and Replication of Oncogenic Viruses: Plaque formation by group B and D viruses on a temperature-sensitive Rous sarcoma virus-infected cell is being employed to investigate the size and nature of virus-specific DNA in infected cells. Very early forms of virus-specific nucleic acids such as RNA-DNA hybrids or duplex DNA may be formed by this method; Conventional cell fractionation followed by nucleic acid preparation and analysis will be used to trace the fate of parental RNA from Rous sarcoma virus (RSV). Temperature sensitive mutants of Rous sarcoma virus provide one means to control these experiments; since no steps from DNA onward occurs in infections with mutants that contain a temperature sensitive DNA polymerase, a comparison of the biochemical and biophysical nature of parental RNA at various times after infection at the permissive and nonpermissive temperatures should serve to elucidate significant events in the fate of parental RSV RNA; Specific labeling of cell surface components by membrane-impermeable reagents will be attempted in an effort to study membrane changes that occur in association with virus-induced cellular transformation. Temperature-sensitive mutants of RSV will be used to detect subtle changes which are unique to the transformed phenotype.